Isomerization process



Patented Aug. 28, 1945 Eur OFFICE.

' IsoMEnIzA'noN PROCESS Charles S."Lynch, Plainiield, J assignor to Standard Oil Development Company, 'a corporation of Delaware No Drawing. Application October '1, 1942, I Serial No. 4 1,121

roams. (Cl. zen-683.5)

The present invention relates to the isomerization of straight chainor normal paraflinic l vdrocarbons to produce the corresponding iso or branched chain parafllnic hydrocarbons. More particularly, the invention is concerned with the isomerization of those hydrocarbons which have heretofore been considered as being readily decomposed when subjected to isomerization reactions. Particularly these feed stocks embody straight chain paraflins containing at least five carbon atoms per molecule, and.the isomerizationis carried out in the vapor phase using Friedel- Crafts type catalysts. and halogen-containing promotors or substances whichproduce such promoters in situ. a a

In the isomerization of normal parafllnsof at least five carbonatomsper molecule to their corresponding branched chain isomers various Friedel-Crafts type catalysts have been employed either with or without .the addition of various promoters such as hydrogen chloride, hydrogen bromide, chlorine, bromine, carbon tetrachloride, chloroform, the lower alkyl halides such as methyl, ethyl, propyl and the butylchlorides and 1 bromides, and the like. Small amounts of water and substantial amounts of molecular or free hydrogen have likewise been employed and heretofore these reactions have been chiefly carried out in the liquidphase using suflicient superat- I mospheric ,pressures'rto maintain liquid phase operation. The present invention embodies the use of such catalysts and promoters but is concerned with a. vapor phase type of operation. These operations are known to the art and are usually carried out using a bed type of reactor in which a porous carrier has sorbed thereon a suitable Friedel-Crafts type catalyst and the reactions are carried out under correlated temperature and pressure conditions so that the feed stock and promoter which are admixed and passed to the reactor isomerizeand the desired isomers are recovered from the reacted mixture.

While such vapor phase operations have been found entirely practical for the isomerization of normal butane to isobutane, their application to processes involving the higher homologues of normal butane has been found quite dimcult. Normal butane offers some considerable, degree of resistance to cracking and degradation and hence does not decompose readily when subjected to temperatures of from .300 F. to 400 F., these temperatures being those commonly employed in vapor phase isomerizationreactions.- On the other hand, however, normal pentane isquite susceptibie to cracking when subjected to such temperatures inthe presence of Frledel-Crafts type catalysts such as aluminum chloride and the usual halogen-containing promoters and so'it was heretofore thought necessary to carry out the vapor phase isomerization of normal pentane toisopentane at temperatures considerably below.

those mentioned for normal butane isomerization, namely, in the neighborhood of about F. to about 225 F. Such a process, however. is not conducive to commercial yields of isopentane because orthe fact that the rate of isomerization of normal pentaneto isopentane is considerably slower at these lower temperatures than is the "case when higher temperatures are employed, but

comes-- contaminated withtarry residues and quickly loses its catalytic activity so that the degradation of the feed stock has a corollary the degradation of the catalyst activity. Heretofore the introduction of substantial amounts of molecular hydrogen pressure has helped to some extent to minimize the excessive cracking and degradation of the normal parafllns containing five or more carbon atoms per molecule but this has not been the complete answerand doesnot eliminate the production of extremely low yields of isoparamns. The amount of normal parailln converted is oftentimes materially reduced by the introduction of large quantities of hydrogen and in this case it is readily apparent thatthe amount oflisomerization is decreased in order to avoid the degradation. r m p H It is an object of the present invention to materially increase the yields of desired isomeric.

branched chain parafllns containing at least five carbon atoms per molecule 'from their corresponding straight chain or normal paraiilns while properly correlating the reaction conditions so that the rate of isomerization is substantially that employed in vapor phase isomeriza'tion or normal butane to isobutane and at 'thelsame'time substantial degradation of the feed stock and resulting contamination of the catalyst is materially decreased and at times substantially completely avoided. It is afiurther object of the invention to not only secure increased yields of the desired isomers but also to improve the selectivity of the isomerization reaction. In effect, this means that for every mol of normalpentane undergoing isomerization more nearly one mol of isopentane is recovered therefrom; or, to define selectivity in another way, it is the number obtained by-dividing the percentage of isopentane obtained in a given reaction .by the percentage of normal butane undergoing reaction and multiplying. the :result;

by 100. .In other words, if every mol of normal pentane were isomerized to one moi of isopentane W the selectivity would be 100. It is a further object of the invention to increase the overall em ciency of isomerization reaction as measured in gallons of isoparaflin produced per poundlof aluminum halide'employed. Other objects will be apparent from a fuller understanding of the invention.

In carrying out the invention a. salient feature of the same resided in the discovery that it is now 4 possible'to employ temperatures ranging between about 400 F, and about 500 F. in the isom'eriz'ationo'f normal. pentane to isopentane while at the same time avoiding excessive degradation or -.crfacking of the feedstock and consequent "contamination of the catalyst with tarry masses if theother reaction conditions are properly correlated when these heretofore considered detri-- mentalhigh'temperatures are used. It has been discovered ,that whereas temperatures of I from 150'. F. to 225 I". haveheretofore been employed forthevapor phaseisomerization of normal pen tamination and tarring of the catalyst. The catlyst is usually aluminum chloride or aluminum.

pregnated'on and sorbed in the carrier to the extent of. between about 4% and about 12% althoughjamounts-of aluminum chloride outside oi these ranges may be employed if desired. A hum berof methods may be employed for impregnating or sorlbing the aluminum chloride in the porous carrier, for example Porocel, This may be done by vaporizing aluminum chloride and passing the vapors in the presence of a carrier gas.

such as nitrogen, carbon dioxide, chlorinebromine, hydrogen chloride, hydrogen bromide, hy-' drogen,or thelike, into contact with the'Porocel which has previously been heated to a temperature of from 1000 to 1400 F. for from 1 to 18 time to isopentanevery low yields'ot the desired isopentane'are secured andthat although it was knownthat the rate of isomerization could be 1 increased by increasing the' temperature of the reaction it hasnow been discovere'd that not only i is the'rate of is'oinerizationincreasedfbut the selectivityjof the final product has been found to have'be'en increased as well. Thus, for example, under-comparable conditions in-any given reaction in whichv 20% of normalj pentane is're'acted at a temperature of aboutf'325 Eonly'a'bo'ut of that amount of normal pentane was found to have been converted to isopentane, whereas un dejr thesa'me conditions except when employing a temperature or; 400 1F. and wherein 20% or the normal pentane reacted, fofflthis same amount of normal pentane was found to; have been converted to isopentajne. Under still more hours before thoroughlydrying the same, or the Porocel may have lumps of aluminum chloride admixed with it and the same heatedto disperse the vaporsof aluminum chloride through the Porocel mass. Still a second alternative resides in the use ofa suitable solvent for the aluminum chloride suchas ethyl chloride, ethylene dichloride, dioxane, and the like,-so that a solution of aluminum-chloride in the solvent is contacted with'the Poroceixand after a suitable lengthof time the mass is drained of excess liquid and heated to drive-oi! the solvent contained therein, aving behind in the pores oi the carrier the aluminum'chloride. v.

The invention is -not restricted to, any particular method of catalyst formation so long aszthe solid bed-type of catalyst mass is employed. -=Aldrastie'reaction conditions' wherein 40% "of the penmne feed was reacted at a temperatufeof 3257's., boutzzm r that 40% reacted foun'd to be isopentane; whereas at 400 F.

about 57% of the 40% reactedwas foundto have been converted to "isoperitarie; In other words,

' whereonly] small amountsof normalpentane are reacted, the selectivity variation between the two temperatures of 325i- F. and 400 F. represents selectivityof only'about '16 or 17, yet at? a.v point where 40% of the: normal, pentane is reacted thespread in selectivity'is evengreater as between 3257'. FL and 400 E. and represents a difle'r'ential ofabout 20 in the selectivity. Even whenoperating at temperatures'as high as 500 F. the selectivity and conversion are'improved n s o ar r mn ql di 7 l h Inprderto these results," however.

itfifs necess'ary ftliatthereaction conditions, cata =l'y'stactivltY, etc; be carefully correlated withrespecttoone another'sothat the marked increase though not a particularly-advantageous wayto carry out the invention, it iswithin the contemplationoi the present process to employ a solid catalyst mass composed entirely of lumps or granules or pellets of solid aluminumchloride. Such a process, however, is not feasible because ofthe consequent plugging of lines, valves, towers and thelike with condenser vapors of aluminum chloride. In preparingthe aluminum chloride on porous carriers it is ofttimes desirableto subject .over. that"obtained at 325 1". orat temperatures of from 150? ,F. 225 F.s uchas haveheretofore in-ftemperature does'nqt result in an increased degradation of the stock and resulting conthe resultant aluminum chloride-Porocel mass to temperatures offrom 25 to higher than that to be encountered in the isomerization reaction and to pass-inert carrier gases therethrough in order to remove any loosely held aluminum chloride so that the catalystactually employed is a carrier containing only'tenaclously held aluminum chloride and no large amount of vapors of aluminum chloride are then given of! durinB the carrying out of the isomerization reaction.

The feed stock employed in conjunction with the present process may bequite'vari'ed. Normal pentane,-normal hexane normal heptane and the higher straight chain -homologues may be emplayed or mixturesot two or. more of thesemay be employed. Also, casing-head gasoline and other-straight run naphthas obtained either from 2,983,609 natural gas orfmm petroleum distillates m'ay likewise be mployed. The process is chiefly concemed with the-conversion of normal pentane to isopentane but a modification of reaction conditions is possible to convert normal hexane to isohexanes, and so forth. It is not necessary that th feed stock be 100% normal pentane but it may contain small amounts of isopentane and still be suitable for the process.

In order to preserve the life of the aluminum chloride catalyst mass it has been found desirable t pretreat feed stocks employed in order to'remove therefrom excessive amounts of water and to also remove olefins, sulfur compounds and the like which are frequently inassociation with the feed stocks. The olefin and water are removed first by treating with concentrated sulfuric acid of the order of 90 to 98 or by the use of suitable strengths of fluosulphonic or chlor-sulphonic acid. jGaustlc solutions may be employed for the removal of sulfur compounds.

The isomerization is usually carried out .in the presence of any one or more of the promoters heretofore mentioned and theymay be employed where elemental or free hydrogen is em- 7 ployed and this is generally used' in amounts ranging between about 50 and about 600 lbs./sq. in. of partial pressure of free or molecular hydrogen, preferably in amounts ranging between about 100 and about 250 lbs/sq. in. partial pressure.

varies considerably dependingupon the specific temperature employed and. it is quite important that the feed rate be substantially constant for any given run in order to control accur'atelythe conversion so as to avoid excessivedegradation. In general, where the temperature ofthe reaction is maintained between about 325 Rand 550 F. the throughput varies between about 0.25 and about 2 volumes of liquid normal parafiin per volume of catalyst mass per hour, or, in other words, the time of contact may range as much as from 16 to 260 seconds, preferably between about and about 1'75 seconds, when a preferred temperature of between about 400 F. and about 500 F. is employed.

The proper superatmospheric pressure to be employed is usually determined by the eiflciency of separation of the hydrogen halide or other suitable gaseous promoters in the stripping tower of catalyst masses therein and through which the vapors are allowed to pass. The reactor may be jacketed or coils may be placed inside 'the reactor proper as accurate temperature control means. The reactor may be a single one or a plurality of, reactors arranged in either series or parallel and the feed stock may be continuously fed to'one of these reactors even though the others maybe on stream for the removal or for the regeneration of spent catalyst. In the regeneration of the catalyst the mass is usually heated to drive oif any aluminum chloride vapor that can be driven off and the carbonaceous residues are then subjected to a burning opera-- tion at temperatures of 700-1000 F. coupled with the passage of free oxygen or free-oxygen-containing gases diluted with carbon dioxide, hydrogen or some inert material, therethrough to remove and burn the carbon therefrom. Once the pores of the carries are free, aluminum halide vapors may be introduced into the carrier and the same reimpregnated in conventional manner.

The following examples are given in order to aflord a clearer understanding of the character of the invention, although it is vto be distinctly understood that the invention is not limited thereto.

' wEzrample 1 An isomerization catalyst was prepared ,by charging to a closed tubular reactor about gramsof anhydrous aluminum chloride and'sufficient Porocel-whichhad previously been heated to a temperature of about 1100 F. for about 15 hours to form afinal composition of about 8.8%

aluminum chloride on' the Porocel. The mix- The time of contact employed in the reaction from the reacted mixture, although the pressure in the stripper is not necessarily the same as that maintained in the reactor. In general, the reaction is maintained under suflicient superture was placed in the continuous reactor'and sealed in. A mixture of normal pentane containing between 5 and 6' weight per cent of hydrogen chloride was then passed through this reactor which was maintained at about 400 F. under a pressure of about85 lbs./sq. in. The rate of addition of the normal pentane was at'between about 0.49 and about '1 liquid volume of normal pentane per volume of catalyst per hour. This corresponded to a contact time of between about 33 and about 64 seconds; This operation was continued for a total of 12 hours and, at approximately hourly periods a sample of vthe reacted mixture was withdrawn and analyzed for isopentane production and it was found that the isopentane varied between 10% and 16% of the final product and that the selectivity of the reaction varied between about 41 and 75 with an average yield of isopentane of 13% and an average selectivity of 61%. The yield of gallons of isopentane per pound of aluminum chloride was about 1.8.

atmospheric pressure to maintain an easy stripping operation and at the same time if molecular or free hydrogen is employed then still higher pressures up to as high as 1000 lbs/sq. in. total pressure may be used.

No special type of apparatus or construction is necessary in carrying out the process of the present invention. It may be carried out on either a batch scale or continuous type of operation, although its highest utility is to be found in the commercial continuous type of operation. The reactors are generally of the type employed for solid catalyst operation wherein perforated plates or baskets are employed for the retention ,of isopentane was only 15%, with the lowest being 1%, and that the selectivity varied between 37 and 88 with the average selectivity being 48% and the average yield of isopentane 0%.

gallon per pound of aluminum chloride.

In another run wherein the temperature F. and the throughput about 0.3 v./v./ the product analysis showed at the most 1% yield of isopentane in 2 hours of operation but the deg- The yield of isopentane amounted to 0.9

4 radation was quite excessive. since, the product contained 12% of C4 and 'lighter hydrocarbons. In still another operation using a temperature of 200 F. and a gauge pressure of 25 lbs/sq. in.

with a throughput no.5 v./v./hr., less than 3% of lsopentane was obtained. in the period of 6 to 8 hours of running and only 8% of isopentane was obtained in thefirst' 2 hours'of operation. The selectivity in this'tirst 2-hour period was roughly about '30. r j

. Exomplez A'nother run was carried out at 400 F. in a manner'similar to that described in the first example and run for a total of 24'hours under pressures varyingbetween '35 and 180 lbs/sq. in. and

th'e 'ieed ratesranging between about 0.25 and 1 v./v ./hr. The yieidof isopentane averaged 16% and the selectivity averaged 54. --'The overall,

with a yield of about 1.8gallons of isopentane Wis-p und of aluminum chloride. j

Saving thus described illustrated the characterot the invention, what is desired to be secured yf Ietters'Patent lei 1, The process which comprises isomerizing normal pentane in the vapor phase under isome'rization reaction conditions in, the presence of promotional amounts oi halogen-containing promoter and inthe' presence of aluminum chloride, the temperature or the reaction being mainvapor phase isomerlzation of normal pentane in the presence of aluminum chloride and a hydrogen halide "promoter under superatmospheric temperatures and pressures; which comprises maintaining the temperature of the isomerization reaction between about 400 F. and about500 F.

" at a throughput of between about 0.25 and about 1 volume of liquid normal pentane per volume of catalyst per hour under a pressure of between about 2 and about 12 atmospheres while permitting the normal pentane vapors to flow through a catalyst bed of aluminum chloride sorbed in a partially dehydrated, calcined bauxite, said vapors having admixed therewith between about 4 and about 8 weight per cent of hydrogen chlotained at between about 4009 1. and about 500 F.

and the throughput between about 0.25and about 1 volume of liquid normal pentane per volume orcatalyst per hour while. correlating the'reac tion ,conditions to secure the lcorresponding branched chain paramns asfthe predominant product of the reactions 2. A process of increasing the yield of isopentoneper moi otnormal pentane reacted in the ride, and recovering isopentane from the reacted mixture.

5. A process as in claim 4 wherein the catalyst masscontains between about 8 and about 12% of aluminum chloride and wherein between about 0.005 and about 0.04 weight 'per cent of aluminum chloride vapor is added to the reaction zone by admixture with the normal pentane feed in order to maintain catalytic activity of the isomerization catalyst mass. 1

6.A*=processtor the isomerization of normal pentane which comprises contacting vapors of normal'pentahe containing between about '4 and about 8 weight per cent of hydrogen chloride at a space velocity of between about 0.49 and about 1 volume of liquid normal pentane per volume or catalyst perhour at a temperature between about 400 F. and about 500 F. in contact with aluminum chloride-present in a porous carrier in the amount of between about 4 and about 12% by weight. and recovering isopentane from. the

reacted mixture.

CHARLES S. LYNCH. 

